1. Field of the Invention.
This invention relates to a mechanism for urging an electrostatic recording medium towards a multi-stylus electrode head in an ordinary paper, image-transcribing, electrostatic recording system. In such a system, electrostatic latent images are formed on the electrostatic recording medium by the multi-stylus type electrode head and the latent images are then developed, transferred on an ordinary paper sheet, and finally fixed.
2. Description of the Prior Art.
A conventional electrostatic recording system has recording styli arranged in one direction at a high density. High tension image signals are applied to the recording styli (charging electrodes) thus forming electrostatic latent images on an electrostatic recording medium in accordance with the image signals creating the electric charge. The electrostatic latent images thus formed on the electrostatic recording medium are then fixed.
In the conventional recording system, a so-called matrix driving is effectuated to reduce the voltage applied to the recording electrodes and also to reduce the driving drivers. For the realization of such a drive, auxiliary electrodes 3 are placed in the vicinity of the charging electrodes 2 as shown in FIG. 1 thus obtaining a multi-stylus electrode known as a Gould type.
In addition to the above described arrangement, there is an arrangement wherein auxiliary electrodes are provided on the other side of the electrostatic recording medium (recording paper) and this arrangement is known as a Philip type multi-stylus electrode.
In either of the above arrangements of the multi-stylus electrode, a gap of from 4 to 12 microns is always required between the charging electrodes 2 and the surface of the recording medium.
In order to maintain the above described gap, FIG. 2 shows a method wherein projections of about several microns are formed on the surface of the recording paper 5 and a rubber or sponge roller 6 is used to depress the recording paper 5 from the rear side thereof in order to urge the paper 5 to the multi-stylus electrode 1 while the projections insure that the required gap is maintained.
In addition to the above described method for directly forming images on the recording paper, image transferring recording methods have been recently developed wherein a recording medium 7 as shown in FIG. 3 is used. The recording medium 7 comprises a recording layer 8, an intermediate resistance layer 9, and a base layer 10. Electrostatic latent images are formed on the recording layer 8 and these images are developed by a xerographical method utilizing toner. The toner image is then transferred on an ordinary paper sheet and the image remaining on the recording layer 8 is cleaned so that the recording layer is ready for a subsequent recording operation.
The applicant of the present invention has previously proposed a method for maintaining the gap between the charge electrode 2 and the recording layer 8 as shown in FIG. 3. In FIG. 3 a coating 11 which is several microns thick is applied to a part of the electrode corresponding to the auxiliary electrodes. The coating 11 is not applied to the part corresponding to the charge electrode as explained in Japanese Patent Application No. 163591/1979).
In this method, since it is intended to maintain the gap by the thickness of the coating 11, it is required that the recording medium 7 be held in tight contact with the multi-stylus electrode assembly 1 along the entire surface of the length of the assembly. FIG. 4 is a perspective view showing the lengthwise part of the same assembly.
To maintain the recording medium in tight contact with the multi-stylus electrode assembly, a rubber roller and a sponge roller shown as reference numeral 6 in FIGS. 2 and 3 has been used. However, it has been found that with the hardness of the rubber rollers currently available on the market, it is impossible to provide uniform contact between the recording medium and the electrode assembly along the entire length of the latter.
The hardness of the sponge roller can be made lower than that of the rubber roller thus enabling one to provide the desired uniform contact between the recording medium and the electrode assembly along its entire length. In this case, however, it is required that the engaging portion between the two members has a width larger than that designated by D in the multi-stylus electrode assembly of FIG. 3 thus requiring an excessively large outer diameter of the sponge roller which is not desirable from the viewpoint of reducing the size of the overall apparatus.
Although the width of the engaging portion can be increased by increasing the urging force of the sponge roller toward the electrode assembly, such a procedure is not desirable because the excessive force required tends to shorten the operable life of the gap maintaining coating 11. A procedure utilizing an endless belt 12 instead of the rubber roller for increasing the width of the engaging portion is disclosed in Japanese Patent Laid-Open No. 1625/1979 and shown in FIG. 5. Although the width of the engaging portion itself can be somewhat increased, this procedure is not advantageous because it complicates the apparatus and makes it rather large thereby increasing the production cost of the apparatus.